With an ever increasing awareness among the public as to the privacy of digitally stored data, much attention has been focused on mechanisms for providing secure files and/or file access. Such security may become ever more important as, for example, more and more information is stored in a “file server” format. For example, with the recent introduction of publicly accessible “Internet hard disks” where files of many different, and often unrelated, users are stored on Internet accessible servers, the issue of file security may become even more important. As is evidenced by, for example, the systems identified below, many differing solutions have been proposed to the problem of file security.
One conventional file security system is described in Allen G. Konheim, Cryptography, A Primer, John Wiley & Sons, New York, 1981, pp. 348–363, which describes a file security system called the Information Protection System (IPS). In IPS, each user has a secret passphrase, which is hashed by the system to produce a file encryption key. The file encryption key is then used to encrypt/decrypt that user's files. The encrypted files for all users are stored in a common system database. Each enciphered file has a file header. The file header contains such information as the type of encipherment used, a time-date stamp, the version of IPS employed, cryptographic chaining information and a key verification field, but it contains no encrypted key field, since IPS uses only a 1-level key management system.
Additional security systems are described in U.S. Pat. Nos. 4,238,854, 4,757,533, 5,150,407, 5,235,641, 5,495,533, 5,563,946, 5,699,428, 5,719,941, 5,751,814, 5,787,169, 5,841,871, 6,011,847 and 6,023,506.